Flying-circus

Changed
* Create some introductory documentation
* Update AWS Resource specification to v2.25.0
* Create classes for all AWS services
* [171](https://github.com/garyd203/flying-circus/issues/171): Support
`UpdateReplacePolicy` and introduce `is_retained` property for a resource.

Changed
* Update AWS Resource specification to v2.22.0

Changed
* Added changelog
* Refactor AWSObject to use `attrs` for attribute access. The way you define
an AWSObject subclass has changed (especially Resource classes).
* Remove installation dependency on `boto3`
* Hide code from original proof-of-concept implementation (`fcspike`) so that
it is not part of a standard installation.